Compressing radio maps

ABSTRACT

Embodiments are disclosed for compressing radio maps of fingerprint-based positioning systems. In an embodiment, a method comprises: receiving access point (AP) data from a plurality of mobile devices operating in a geographic region, the AP data including signal strength measurements of AP signals received at a plurality of reference locations in the geographic region; filtering the AP data to remove outlier AP data; fitting a surface to the AP data; projecting AP data at surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the AP data at the surface control points; encoding the boundary; encoding the AP data at the surface control points included within the boundary; generating compressed radio maps from the encoded AP data; and responsive to a request from a mobile device operating in the geographic region, sending a data packet including the compressed radio maps to the mobile device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 62/514,759, filed Jun. 2, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to fingerprint-based positioning systems.

BACKGROUND

Outdoor positioning systems typically cluster harvested access point (AP) signal measurements from a large number of mobile devices. Because outdoor positioning systems rely on satellite signal visibility, the clustering approach does not work indoors or in outdoor spaces where satellite signals are blocked or where the quality of satellite signals is poor due to multipath. One solution for improving outdoor localization in spaces with poor signal reception is to use indoor positioning techniques to estimate location. For example, an outdoor space, such as an “urban canyon,” is divided into a grid. The grid can be irregularly shaped and include cells that have no signal data or only sparse signal data. In this case, the grid includes a large number of radio maps, where the radio maps include “fingerprints” collected at reference locations within the outdoor space, and each fingerprint includes an identification and received signal strength of the APs observable at the reference location. Due to the high cost of cellular data service and the limited storage capacity of the typical mobile device, it is desirable to compress the radio maps before serving the radio maps to mobile devices for use in location estimation.

SUMMARY

Embodiments are disclosed for compressing radio maps of fingerprint-based positioning systems.

In an embodiment, a method comprises: receiving, by a computing device, AP data from a plurality of mobile devices operating in a geographic region, the AP data including signal strength measurements of AP signals received at a plurality of reference locations in the geographic region; filtering the AP data to remove outlier AP data; fitting a surface to the AP data; projecting AP data at surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the AP data at the surface control points in the image grid; encoding the boundary; encoding the AP data at the surface control points included within the boundary; generating compressed radio maps from the encoded AP data; and responsive to a request from a mobile device operating in the geographic region, sending a data packet including the compressed radio maps to the mobile device.

In an embodiment, a system comprises: one or more processors; memory coupled to the one or more processors and configured to store instructions, which, when executed by the one or more processors, causes the one or more processors to perform operations comprising: receiving AP data from a plurality of mobile devices operating in a geographic region, the AP data including signal strength measurements of AP signals received at a plurality of reference locations in the geographic region; filtering the AP data to remove outlier AP data; fitting a surface to the AP data; projecting AP data at surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the AP data at the surface control points in the image grid; encoding the boundary; encoding the AP data at the surface control points included within the boundary; generating compressed radio maps from the encoded AP data; and responsive to a request from a mobile device operating in the geographic region, sending a data packet including the compressed radio maps to the mobile device.

Particular embodiments disclosed herein provide one or more of the following advantages. The disclosed embodiments allow compression of radio maps delivered in tiles to mobile devices for use in location estimation. The compressed radio maps reduce the cost of cellular data service for users and also reduce the amount of data stored on mobile devices which often have limited storage capacity. Additionally, the multiple versions of tiles with different resolutions can be generated to mobile devices based on memory and processing constraints of the mobile device and a desired location estimation accuracy.

The details of one or more implementations of the subject matter are set forth in the accompanying drawings and the description below. Other features, aspects and advantages of the subject matter will become apparent from the description, the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example fingerprint-based positioning system (FPS), according to an embodiment.

FIG. 2 is a flow diagram of a server-side FPS processing pipeline, according to an embodiment.

FIG. 3 is a flow diagram of a client-side FPS processing pipeline, according to an embodiment.

FIGS. 4A-4C illustrate surface fitting to AP data, according to an embodiment.

FIGS. 5A-5C illustrate contour detection and blob boundary encoding, according to an embodiment.

FIG. 6 is a flow diagram of a process of generating compressed AP radio maps, according to an embodiment.

FIG. 7 is a flow diagram of a process of surface fitting and encoding, according to an embodiment.

FIG. 8 illustrates an example server architecture, implementing the service-side FPS features and operations described in reference to FIGS. 1-7.

FIG. 9 illustrates an example device architecture of a mobile device implementing client-side FPS features and operations described in reference to FIGS. 1-7.

DETAILED DESCRIPTION Example Fingerprint-Based Positioning System

FIG. 1 illustrates an example FPS system 100, according to an embodiment. System 100 includes FPS server computers 102, mobile device 103, network 104, access points (APs) 105 and radio map database 106. RF signals transmitted by APs 105 are measured by mobile devices 103 operating in various geographic regions. An RF signal measurement is typically in the form of a received signal strength indicator (RSSI), which is the metric used by the embodiments described herein. It should be noted, however, that other measurements of RF signal strength can be used with the disclosed embodiments.

FPS 100 harvests AP data packets from a large number of mobile devices 103 to build FP database 106. The AP data packets include AP data for a particular reference harvest or survey location in the geographic region, also referred to herein as “reference location.” An AP can be any wireless network AP, including a WiFi router or a cell tower transmitter. The AP data typically includes position data for the reference location (e.g., latitude, longitude, altitude, position uncertainty) provided by a survey map, global navigation satellite system (GNSS) receiver, WiFi position system or cell tower trilateration. The AP data also includes RSSI values and media access control (MAC) addresses for APs that are observed (scanned) at each reference location. If available, the AP data also includes GNSS velocity and/or pedestrian dead reckoning (PDR) data generated from equations of motion on mobile devices 103, such as position, velocity (speed) and heading. The PDR data can be generated from inertial sensor data provided by inertial sensors on the mobile device (e.g., accelerometer, gyro, magnetometer). Some AP data may also include barometric pressure data (e.g., provided by a pressure sensor on the mobile device) that can be used to indicate the altitude of the reference location.

FPS servers 102 calculate probability distributions of the RSSI values (e.g., Rayleigh, Rician, Gaussian distributions, etc.) for each AP observed at each reference location. The radio maps are stored in radio map database 106. In response to a request from a mobile device, FPS server computers 102 download a data packet or “tile” to the mobile device that includes compressed radio maps as described in further detail below in reference to FIG. 2

FIG. 2 is a flow diagram of a server-side FPS processing pipeline 200, according to an embodiment. Pipeline 200 includes AP filter 202, AP signal filter 203 and radio map generator 204. AP data 201 is collected from a large number of mobile devices and initially stored in a database separate from the FPS production system.

AP filter 202 determines whether AP locations in AP data 201 are servable or not-servable to mobile devices. AP locations that are servable are sent to mobile devices for use in location estimation. AP locations that are not servable are not sent to mobile devices for use in location estimation. An AP location is not servable if, for example, the AP location has moved over a specified time period, or a portion of outlier AP data is too high even if the estimated position of an AP has not moved. In an embodiment, AP data 201 can be clustered and APs that have moved between clusters are moving APs. Some examples of suitable clustering algorithms include but are not limited to: DBSCAN, k-means and hierarchical cluster analysis (HCA). A technique for identifying moving APs is described in U.S. Patent Application No. 62/509,562, filed on May 22, 2017, which provisional patent application is incorporated by reference herein in its entirety.

In an embodiment, an AP may be excluded from further processing based on memory cost, sighting probabilities and/or coverage. For example, each AP can be ranked based on a score that is a function of memory cost, cumulative sighting and probability over all cells. The APs can then be included in, or excluded from, further processing based on their scores. In an embodiment, a greedy algorithm can be used to determine scores.

AP signal filter 203 receives the filtered AP data from AP filter 202 and clusters the RSSI values in the AP data to identify outlier RSSI values. For example, RSSI values that are less than a minimum threshold and greater than a maximum threshold may be considered outlier RSSI values and excluded from further processing. Some examples of suitable clustering algorithms include but are not limited to: DBSCAN, k-means and HCA.

Radio map generator 204 receives the AP data output by AP signal filter 203 and performs surface fitting to generate RSSI and uncertainty maps, as described in reference to FIGS. 4 and 5. In an embodiment, radio map generator 204 also generates tiles 205 including radio maps 206 having different resolutions based on tradeoffs between mobile device memory and processing constraints and location estimation accuracy. To achieve different resolutions, some of tiles 205 may include more radio maps 206 than other tiles 205, or have different cell sizes. For example, a tile created for a dense urban environment may have more radio maps than a tile for a rural environment. Or, in another example, an open parking lot adjacent to a mall may need a lower cell resolution than the cell resolution used in the mall.

FIG. 3 is a flow diagram of a client-side FPS pipeline 300, according to an embodiment. Tiles 301 for a geographic region, which were generated using pipeline 200, are pre-fetched or downloaded on-the-fly to a mobile device operating at a location (x, y) in a geographic region. In an embodiment, selected ones of tiles 301 that match the memory or processing constraints of the mobile device and desired location accuracy for the location (x, y) are used for localization.

When an AP is observed at location (x, y), RSSI lookup module 302 decodes and decompresses radio maps 206 that are included in tiles 301 and stores them in local cache memory. An RSSI prediction at location (x, y) is then computed using an interpolation function f (x, y) using the RSSIs at the surface control points. In an embodiment, the function f (x, y) is bilinear and the RSSI values at the four surface control points (Q11, Q12, Q21, Q22) that are nearest to location (x, y) are used in the bilinear interpolation function f (x, y) as shown in Equations [1] and [2].

$\begin{matrix} {{{f\left( {x,y} \right)} \approx {{b_{11}{f\left( Q_{11} \right)}} + {b_{12}{f\left( Q_{12} \right)}} + {b_{21}{f\left( Q_{21} \right)}} + {b_{22}{f\left( Q_{22} \right)}}}},} & \lbrack 1\rbrack \\ {\begin{bmatrix} b_{11} \\ b_{12} \\ b_{21} \\ b_{22} \end{bmatrix} = {{\left( \begin{bmatrix} 1 & x_{1} & y_{1} & {x_{1}y_{1}} \\ 1 & x_{1} & y_{2} & {x_{1}y_{2}} \\ 1 & x_{2} & y_{1} & {x_{2}y_{1}} \\ 1 & x_{2} & y_{2} & {x_{2}y_{2}} \end{bmatrix}^{- 1} \right)^{T}\begin{bmatrix} 1 \\ x \\ y \\ {xy} \end{bmatrix}}.}} & \lbrack 2\rbrack \end{matrix}$ where (x₁, y₁), (x₁, y₂), (x₂, y₁), (x₂, y₂) are the locations of the surface control points Q11, Q12, Q21, Q22, respectively, in a blob of RSSI values projected on a two-dimensional (2D) grid, as described in reference to FIGS. 4 and 5. Using Equations [1] and [2] and the RSSI values at the surface control points and their (x, y) locations in the 2D blob, the RSSI prediction at location (x, y) can be computed by localizer 304 of the mobile device, as described below. Because only the encoded RSSI values at the surface control points and their respective locations in the 2D blob are sent to the mobile device (rather than all of the RSSI values in neighboring cells), compression is achieved.

Other interpolation functions can also be used for RSSI prediction, including but not limited to: bicubic, trilinear or spline interpolation. In an embodiment, region quadtrees can be used to lookup radio maps 206 of arbitrary resolutions. A quadtree is a tree data structure in which each internal node has exactly four children. The quadtree can partition a given geographic region recursively by subdividing it into four quadrants or regions. The regions may be square or rectangular or may have arbitrary shapes. In an embodiment RSSI lookup module 302 selects the nearest four (or less) surface control points Q₁₁, Q₁₂, Q₂₁, Q₂₂ in the quadtree whose convex hull covers the location (x, y).

Next, probability distribution generator 303 calculates a probability distribution over location (x, y), where the probability depends on a difference between predicted and observed RSSI values plus uncertainty values. The probability distribution can then be propagated using localizer 304 to generate location estimates 305. Localizer 304 can be any suitable localizer, including but not limited to: a particle filter, Kalman filter or least squares estimator.

In an embodiment, the predicted RSSI values represent a mode parameter of a Rayleigh distribution, e.g., if we take multiple Rayleigh distributions with a single parameter (predicted_rssi). A Rayleigh distribution can be represented mathematically by Equation [3]:

$\begin{matrix} {{{f\left( {x;\sigma} \right)} = {\frac{x}{\sigma^{2}}e^{\frac{- x^{2}}{({2\;\sigma^{2}})}}}},{x \geq 0.}} & \lbrack 3\rbrack \end{matrix}$ where sigma σ is the predicted RSSI (predicted_rssi) and x is the observed RSSI (observed_rssi) to get the conditional probability P(x,y|observed_rssi, predicted_rssi). The predicted uncertainty value α (predicted_uncertainty) is combined with P(x,y|observed_rssi, predicted_rssi) as shown in Equation [4]: final_probability=α*p(x,y| . . . )+(1−α)*prior_probability,  [4] where prior_probability is a fixed tunable parameter.

In another embodiment, it is assumed that predicted_rssi and predicted_uncertainty represent the mean and variance of a Gaussian distribution. In this embodiment, the probability can be found by substituting the parameters x, μ, σ, with observed_rssi, predicted_rssi and predicted_uncertainty, respectively, in Equation [5]:

$\begin{matrix} {{f\left( {\left. x \middle| \mu \right.,\sigma^{2}} \right)} = {\frac{1}{\sqrt{2\;\pi\;\sigma^{2}}}{e^{\frac{- {({x - \mu})}^{2}}{2\;\sigma^{2}}}.}}} & \lbrack 5\rbrack \end{matrix}$

FIGS. 4A-4C illustrate surface fitting to RSSI values, according to an embodiment. As shown in FIG. 4A, surface fitting is performed by surface fitting module 402, which takes as input RSSI values and the associated uncertainty values for a given AP, and outputs RSSI and uncertainty maps 206 (collectively, referred to as “compressed radio maps”) for the given AP. Any suitable interpolation function can be used for surface fitting, including but not limited to: bilinear, bicubic, trilinear and spline interpolation. In the example shown, bilinear interpolation is used.

FIG. 4B illustrates RSSI values 405 for a given AP that are taken from neighboring or contiguous cells (e.g., 7 cells). Any number of neighboring or contiguous cells can be selected based on memory/processing and accuracy tradeoffs. RSSI values 405, when projected onto a 2D image plane, define a 2D blob 404, which bounds the geographic area where RSSI values 405 were harvested/surveyed. Blob 404 can include all of the neighboring cells and/or portions of the neighboring cells and can be any shape and size.

FIG. 4C shows surface 406 fitted to RSSI values 405, resulting from the application of bilinear interpolation and four surface control points. In an embodiment, surface control points are at locations (x₁, y₁), (x₁, y₂), (x₂, y₁), (x₂, y₂) in blob 404. Any suitable locations for the surface control points can be used. In the example, corners of grid cells are used. RSSI values 407 a-407 d at the surface control locations (the values f(Q₁₁), f(Q₁₂), f(Q₂₁), f(Q₂₂) in Equation [1]) and their respective locations ((x₁, y₁), (x₁, y₂), (x₂, y₁), (x₂, y₂)) can then be encoded, as described in reference to FIGS. 5A and 5B, to achieve compression gain.

In an embodiment, the surface control points can be selected as points on a regular 2D grid, as shown in FIG. 4C. In other embodiments, surface control points are selected using an iterative end-point fit algorithm (e.g., the Ramer-Douglas-Peucker algorithm) or any other known algorithm that can be used for selecting surface control points (e.g., Visvalingam-Whyatt, Reumann-Witkam, Opheim simplification, Lang simplification, Zhao-Saalfeld).

In an embodiment, bilinear interpolation can be achieved more efficiently using a cell adjustment process. First, a course grid is selected and bilinear fitting is performed on RSSI values in the coarse grid. For each set of N neighboring cells in the coarse grid (e.g., four neighboring cells), a joint likelihood of the RSSI values falling between the N cells is computed. If the joint likelihood is below a threshold, the N cells are divided in half to create a finer grid and bilinear fitting is performed again on the finer grid. This dividing and surface fitting process continues until the joint likelihood of the N neighboring cells is greater than or equal to the threshold, at which point the process stops.

In an embodiment, additional compression gain is achieved by quantizing the RSSI values to a number of quantization levels before surface fitting. For example, the RSSI values can be placed in bins, where each been spans a range of RSSI values. Each bin can be assigned a signal RSSI value (an RSSI quantization level). Each RSSI value that falls within a given bin is replaced by the RSSI quantization level. The quantization levels can be uniform or not uniform. For example, the RSSI range [−100, 0] can be divided non-uniformly into the quantization levels (−100, −50), (−49, −25), (−25, −5), (−5, 0). The quantization levels need not be uniform because the RSSI levels do not necessarily carry the same amount of information.

FIGS. 5A-5C illustrate contour detection and blob boundary encoding, according to an embodiment. For each AP, the RSSI values at surface control points and their associated uncertainties, are input to image processing module 502. Image processing module 502 places the RSSI values and uncertainty values on a 2D image grid and performs contour detection to define blob boundaries. The blob boundaries and the RSSI values and uncertainty values contained in the blobs are input into encoder 503. Encoder 503 encodes the boundaries and RSSI and uncertainty values, resulting in compressed radio maps 504.

Referring to FIGS. 5BA and 5C, RSSI values at surface control points are projected onto image grid 505 (not shown to scale) and processed. Each RSSI value can be represented by one or more pixels 506 in image grid 505. In an embodiment, image grid 505 can be a binary image grid. For example, pixels 506 representing RSSI position data are given a value of 0 (black) and background pixels are given values of 1 (white). To assist the contour detection algorithm, in an embodiment the binary image is morphed using flat dilation (e.g., a Minkowski sum) using, for example, a disk as a structuring element with a specified radius (e.g., 3 pixels).

A contour detection algorithm is applied to the binary image to detect one or more contours from the binary image grid 505, where each contour represents a blob boundary. In the example shown, blob boundaries 507, 508 are detected. Some examples of image contour algorithms, include but are not limited to: square tracing, Moore-Neighbor tracing and radial sweep. In an embodiment, the input into a contour algorithm can be a square tessellation with at least one continuous blob formed from black pixels and the output is a sequence of boundary pixels for the blob. In some cases, there may be more than one blob in the binary image grid.

Blob boundaries 507, 508 are encoded using any suitable encoding scheme, such as predictive differential encoding. Additionally, the RSSI values at surface control points inside blob boundaries 507, 508 are encoded using any suitable encoding scheme, and selection of the encoding scheme can be based on the knowledge of the range of values to be encoded. For example, in an embodiment predictive differential encoding is used to encode the RSSI values in blobs 507, 508, which are typically in dBm and are negative double digit integers (e.g., −70 dBm). Because of the uncertainties associated with the locations of the RSSI values in blobs 507, 508, there are uncertainty regions 509, 510 around blobs 507, 508, respectively. In an embodiment, the uncertainty values associated with locations (x, y) of the RSSI values in blobs 507, 508 are encoded using the same or different encoding scheme. For example, in an embodiment the uncertainty values can range from 0 to 1 (1=no uncertainty) and are encoded using predictive differential encoding or run length encoding. In some implementations, variable Rice coding can be used for encoding RSSI values and/or uncertainty values within blobs. The encoded RSSI values and uncertainties are stored as the aforementioned radio maps 206, which can be served to mobile devices in tiles.

Example Processes

FIG. 6 is a flow diagram of a process of generating compressed AP radio maps based on filtered AP data, according to an embodiment. Process 600 can be implemented by architectures 800 and 900, as described in reference to FIGS. 8 and 9, respectively.

Process 600 can begin by receiving AP data (601). The AP data is received from a plurality of mobile devices operating in a geographic region. In an embodiment, the AP data includes a reference location, RSSI values, RSSI uncertainty values and MAC addresses for each AP observed (e.g., obtained in a wireless scan) at the reference location, a timestamp and optionally other values (e.g., PDR data, barometric sensor data). The reference location can be provided by at least one of survey map data, a GNSS receiver, such a Global Positioning System (GPS) receiver and WiFi or cell tower position data. For example, a GPS receiver can provide the position coordinates (e.g., latitude and longitude) of the reference location in a local-level (geodetic) coordinate system.

Process 600 continues by filtering APs (602). For example, moving APs can be excluded from further processing. In an embodiment, AP locations can be clustered to identify moving APs, as described in reference to FIG. 2.

Process 600 continues by filtering RSSI values (603). For example, RSSI values for an AP that are outside a range define by minimum and maximum thresholds can be excluded from further processing. Also, RSSI values associated with reference locations that have large position uncertainty (e.g., a horizontal position uncertainty greater than a threshold) can be excluded from further processing.

Process 600 continues by generating compressed radio maps (604) as described in reference to FIGS. 4 and 5. The compressed radio maps include AP RSSI and uncertainty maps generated by fitting a surface to the RSSI and uncertainty values. Because only quantized RSSI values at surface control points, and their respective locations in neighboring cells of the 2D grid, are included in the AP RSSI map (rather than all of the RSSI values in the neighboring cells), compression is achieved. The compressed RSSI and uncertainty maps, collectively referred to as compressed radio maps, are stored in a radio map database. The maps can be served to mobile devices in tiles. In an embodiment multiple versions of the radio maps having different resolutions can be stored in a quad-tree to facilitate decoding and decompression on the mobile device.

FIG. 7 is a flow diagram of a process of surface fitting and blob boundary encoding, according to an embodiment. Process 700 can be implemented by architectures 800 and 900, as described in reference to FIGS. 8 and 9, respectively.

Process 700 can begin by receiving RSSI values and associated uncertainty values for an AP (701). The RSSI values can have reference locations from one cell or a set of neighboring cells (e.g., four cells) in a virtual grid dividing a geographic area into cells. In an embodiment, bilinear interpolation can be achieved more efficiently using a cell adjustment process. First, a course grid is selected and bilinear fitting is performed on RSSI values in the coarse grid. For each set of N neighboring cells in the coarse grid (e.g., four neighboring cells), a joint likelihood of the RSSI values falling between the N cells is computed. If the joint likelihood is below a threshold, the N cells are divided in half to create a finer grid and bilinear fitting is performed again on the finer grid. This dividing and surface fitting process continues until the joint likelihood of the N neighboring cells is greater than or equal to the threshold, at which point the process stops.

Process 700 continues by fitting a surface to the RSSI values and the uncertainty values (702). Prior to surface fitting, the RSSI values can be quantized to increase compression gain. In an embodiment, bilinear interpolation is used for surface fitting. Surface control points (e.g., four or less for bilinear) can be selected from the RSSI values based on a desired cell resolution.

Process 700 continues by projecting RSSI values at the selected surface control points to a binary image grid and determining and encoding a blob boundary (703). For example, the RSSI values and associated uncertainties at the surface control points that are projected to the binary image grid can be processed by a contour detection algorithm to determine blob boundaries, which define a geographic region where the RSSI values were harvested/surveyed.

Process 700 continues by encoding RSSI values and associated uncertainty values for an AP using one or more encoding schemes (704). The encoding results in compressed RSSI and uncertainty maps for the AP (collectively, compressed radio maps), which are stored in FP database 106 (See FIG. 1). For example, blob boundaries, RSSI values and their associated uncertainties at the surface control points can be encoded using one or more encoding schemes, including but not limited to: predictive differential encoding, run length encoding and Rice coding.

Example Server Architecture

FIG. 8 is a block diagram of example server architecture 800 for implementing the server-side features and processes described in reference to FIGS. 1-7, according to an embodiment. Other architectures are possible, including architectures with more or fewer components. In some implementations, architecture 800 includes one or more processor(s) 802 (e.g., dual-core Intel® Xeon® processors), one or more network interface(s) 806, one or more storage device(s) 804 (e.g., hard disk, optical disk, flash memory) and one or more computer-readable medium(s) 808 (e.g., hard disk, optical disk, flash memory, etc.). These components can exchange communications and data over one or more communication channel(s) 810 (e.g., buses), which can utilize various hardware and software for facilitating the transfer of data and control signals between components.

The term “computer-readable medium” refers to any storage medium that stores and provides instructions to processor(s) 802 for execution, including without limitation, non-volatile media (e.g., optical or magnetic disks, ROM) and volatile media (e.g., memory, RAM). Computer-readable medium(s) 808 can further include computer program instructions for implementing operating system 812 (e.g., Mac OS® server, Windows® NT server), network communication stack 814, FPS module 816 and tile distribution manager 818 for performing the server-side processes described in reference to FIGS. 1-7. Computer program instructions can be based on any suitable computer language (e.g., C++, Java).

Operating system 812 can be multi-user, multiprocessing, multitasking, multithreading, real time, etc. Operating system 812 performs basic tasks, including but not limited to: recognizing input from and providing output to devices 802, 804, 806 and 808; keeping track and managing files and directories on computer-readable medium(s) 808 (e.g., memory or a storage device); controlling peripheral devices; and managing traffic on the one or more communication channel(s) 810. Network communications stack 813 includes various components for establishing and maintaining network connections (e.g., software for implementing communication protocols, such as TCP/IP, HTTP, etc.).

Architecture 800 can be included in any computer device, including one or more server computers in a local or distributed network each having one or more processing cores. Architecture 800 can be implemented in a parallel processing or peer-to-peer infrastructure or on a single device with one or more processors. Software can include multiple software components or can be a single body of code.

Example Mobile Device Architecture

FIG. 9 illustrates an example device architecture 900 of a mobile device implementing client-side features and operations described in reference to FIGS. 1-7. Architecture 900 can include memory interface 902, one or more data processors, image processors and/or processors 904 and peripherals interface 906. Memory interface 902, one or more processors 904 and/or peripherals interface 906 can be separate components or can be integrated in one or more integrated circuits. The various components in architecture 900 can be coupled by one or more communication buses or signal lines.

Sensors, devices and subsystems can be coupled to peripherals interface 906 to facilitate multiple functionalities. For example, one or more motion sensors 910, light sensor 912 and proximity sensor 914 can be coupled to peripherals interface 906 to facilitate motion sensing (e.g., acceleration, rotation rates), lighting and proximity functions of the mobile device. Location processor 915 can be connected to peripherals interface 906 to provide geopositioning. In some implementations, location processor 915 can be a GNSS receiver, such as the Global Positioning System (GPS). Electronic magnetometer 916 (e.g., an integrated circuit chip) can also be connected to peripherals interface 906 to provide data that can be used to determine the direction of magnetic North. Electronic magnetometer 916 can provide data to an electronic compass application. Motion sensor(s) 910 can include one or more accelerometers and/or gyros configured to determine change of speed and direction of movement of the mobile device. Barometer 917 can be configured to measure atmospheric pressure around the mobile device.

Camera subsystem 920 and an optical sensor 922, e.g., a charged coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) optical sensor, can be utilized to facilitate camera functions, such as capturing photographs and recording video clips.

Communication functions can be facilitated through one or more wireless communication subsystems 924, which can include radio frequency (RF) receivers and transmitters (or transceivers) and/or optical (e.g., infrared) receivers and transmitters. The specific design and implementation of the communication subsystem 924 can depend on the communication network(s) over which a mobile device is intended to operate. For example, architecture 900 can include communication subsystems 924 designed to operate over a GSM network, a GPRS network, an EDGE network, a Wi-Fi™ or WiMax™ network and a Bluetooth™ network. In particular, the wireless communication subsystems 924 can include hosting protocols, such that the mobile device can be configured as a base station for other wireless devices.

Audio subsystem 926 can be coupled to a speaker 928 and a microphone 930 to facilitate voice-enabled functions, such as voice recognition, voice replication, digital recording and telephony functions. Audio subsystem 926 can be configured to receive voice commands from the user.

I/O subsystem 940 can include touch surface controller 942 and/or other input controller(s) 944. Touch surface controller 942 can be coupled to a touch surface 946 or pad. Touch surface 946 and touch surface controller 942 can, for example, detect contact and movement or break thereof using any of a plurality of touch sensitivity technologies, including but not limited to capacitive, resistive, infrared and surface acoustic wave technologies, as well as other proximity sensor arrays or other elements for determining one or more points of contact with touch surface 946. Touch surface 946 can include, for example, a touch screen. I/O subsystem 940 can include a haptic engine or device for providing haptic feedback (e.g., vibration) in response to commands from a processor.

Other input controller(s) 944 can be coupled to other input/control devices 948, such as one or more buttons, rocker switches, thumb-wheel, infrared port, USB port and/or a pointer device such as a stylus. The one or more buttons (not shown) can include an up/down button for volume control of speaker 928 and/or microphone 930. Touch surface 946 or other controllers 944 (e.g., a button) can include, or be coupled to, fingerprint identification circuitry for use with a fingerprint authentication application to authenticate a user based on their fingerprint(s).

In one implementation, a pressing of the button for a first duration may disengage a lock of the touch surface 946; and a pressing of the button for a second duration that is longer than the first duration may turn power to the mobile device on or off. The user may be able to customize a functionality of one or more of the buttons. The touch surface 946 can, for example, also be used to implement virtual or soft buttons and/or a virtual touch keyboard.

In some implementations, the mobile device can present recorded audio and/or video files, such as MP3, AAC and MPEG files. In some implementations, the mobile device can include the functionality of an MP3 player. Other input/output and control devices can also be used.

Memory interface 902 can be coupled to memory 950. Memory 950 can include high-speed random access memory and/or non-volatile memory, such as one or more magnetic disk storage devices, one or more optical storage devices and/or flash memory (e.g., NAND, NOR). Memory 950 can store operating system 952, such as iOS, Darwin, RTXC, LINUX, UNIX, OS X, WINDOWS, or an embedded operating system such as VxWorks. Operating system 952 may include instructions for handling basic system services and for performing hardware dependent tasks. In some implementations, operating system 952 can include a kernel (e.g., UNIX kernel).

Memory 950 may also store communication instructions 954 to facilitate communicating with one or more additional devices, one or more computers and/or one or more servers, such as, for example, instructions for implementing a software stack for wired or wireless communications with other devices. Memory 950 may include graphical user interface instructions 956 to facilitate graphic user interface processing; sensor processing instructions 958 to facilitate sensor-related processing and functions; phone instructions 960 to facilitate phone-related processes and functions; electronic messaging instructions 962 to facilitate electronic-messaging related processes and functions; web browsing instructions 964 to facilitate web browsing-related processes and functions; media processing instructions 966 to facilitate media processing-related processes and functions; GNSS/Location instructions 968 to facilitate generic GNSS and location-related processes and instructions, including processed described in reference to FIGS. 1-7; and camera instructions 970 to facilitate camera-related processes and functions. Memory 950 further includes radio map decoding/decompression instructions 972 for decompressing compressed radio maps. The memory 950 may also store other software instructions (not shown), such as security instructions, web video instructions to facilitate web video-related processes and functions and/or web shopping instructions to facilitate web shopping-related processes and functions. In some implementations, the media processing instructions 966 are divided into audio processing instructions and video processing instructions to facilitate audio processing-related processes and functions and video processing-related processes and functions, respectively.

Each of the above identified instructions and applications can correspond to a set of instructions for performing one or more functions described above. These instructions need not be implemented as separate software programs, procedures, or modules. Memory 950 can include additional instructions or fewer instructions. Furthermore, various functions of the mobile device may be implemented in hardware and/or in software, including in one or more signal processing and/or application specific integrated circuits.

One or more features or steps of the disclosed embodiments may be implemented using an Application Programming Interface (API). An API may define on or more parameters that are passed between a calling application and other software code (e.g., an operating system, library routine, function) that provides a service, that provides data, or that performs an operation or a computation. The API may be implemented as one or more calls in program code that send or receive one or more parameters through a parameter list or other structure based on a call convention defined in an API specification document. A parameter may be a constant, a key, a data structure, an object, an object class, a variable, a data type, a pointer, an array, a list, or another call. API calls and parameters may be implemented in any programming language. The programming language may define the vocabulary and calling convention that a programmer will employ to access functions supporting the API. In some implementations, an API call may report to an application the capabilities of a device running the application, such as input capability, output capability, processing capability, power capability, communications capability, etc.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub combination or variation of a sub combination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.

As described above, some aspects of the subject matter of this specification include gathering and use of data available from various sources to improve services a mobile device can provide to a user. The present disclosure contemplates that in some instances, this gathered data may identify a particular location or an address based on device usage. Such personal information data can include location-based data, addresses, subscriber account identifiers, or other identifying information.

The present disclosure further contemplates that the entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such personal information data will comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure. For example, personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection should occur only after receiving the informed consent of the users. Additionally, such entities would take any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices.

In the case of advertisement delivery services, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, personal information data. That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, in the case of advertisement delivery services, the present technology can be configured to allow users to select to “opt in” or “opt out” of participation in the collection of personal information data during registration for services.

Therefore, although the present disclosure broadly covers use of personal information data to implement one or more various disclosed embodiments, the present disclosure also contemplates that the various embodiments can also be implemented without the need for accessing such personal information data. That is, the various embodiments of the present technology are not rendered inoperable due to the lack of all or a portion of such personal information data. For example, content can be selected and delivered to users by inferring preferences based on non-personal information data or a bare minimum amount of personal information, such as the content being requested by the device associated with a user, other non-personal information available to the content delivery services, or publically available information. 

What is claimed is:
 1. A method comprising: receiving, by a computing device, access point (AP) data from a plurality of mobile devices operating in a geographic region, the AP data including signal strength measurements of AP signals received at a plurality of reference locations in the geographic region; filtering the AP data to remove outlier AP data; fitting a surface to the AP data; projecting AP data at surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the AP data at the surface control points in the image grid; encoding the boundary; encoding the AP data at the surface control points included within the boundary; generating compressed radio maps from the encoded AP data; and responsive to a request from a mobile device operating in the geographic region, sending a data packet including the compressed radio maps to the mobile device.
 2. The method of claim 1, wherein filtering AP data further comprises: identifying non-servable APs in the AP data; and excluding the non-servable APs from further processing.
 3. The method of claim 1, wherein filtering AP data further comprises: clustering the AP data; identifying outlier AP signal strength measurements based on the clustering; and excluding outlier AP signal strength measurements from further processing.
 4. The method of claim 1, wherein fitting the surface to the AP data further comprises: using bilinear interpolation to fit the surface to the AP data.
 5. The method of claim 1, wherein prior to fitting the surface to the AP data, the AP data is quantized.
 6. The method of claim 1, wherein determining the boundary further comprises: applying contour detection to the projected signal strength measurements at the surface control points; and encoding the boundary using an encoding process.
 7. The method of claim 1, wherein the geographic region is divided into a grid of contiguous cells having a first size and the plurality of reference locations are in a plurality of the contiguous cells.
 8. The method of claim 7, further comprising: adjusting the first cell size to a second cell size based on the AP data.
 9. The method of claim 8, wherein adjusting the first cell size to a second cell size further comprises: (a) fitting the surface to the AP data corresponding to a set of contiguous cells; (b) for the set of contiguous cells, calculating a joint likelihood of signal strength observations falling between the cells; (c) determining that the likelihood is less than a threshold; (d) dividing the set of cells in half; and repeating steps (a) through (d) until the likelihood is greater than or equal to the threshold.
 10. The method of claim 1, wherein the AP data includes AP signal strength measurements and uncertainty values corresponding to the AP signal strength measurements, and the method further comprises: fitting surfaces to the signal strength measurements and the uncertainty values; projecting signal strength measurements and uncertainty values at the surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the signal strength measurements and corresponding uncertainty values at the surface control points in the image grid; encoding the boundary; encoding the signal strength measurements and corresponding uncertainty values at the surface control points that are included within the boundary; and generating compressed radio maps from the encoded signal strength measurements and corresponding uncertainty values and the encoded boundary.
 11. The method of claim 10, wherein the encoding scheme is at least one of predictive differential encoding, run length encoding or Rice encoding.
 12. A system comprising: one or more processors; memory coupled to the one or more processors and configured to store instructions, which, when executed by the one or more processors, cause the one or more processors to perform operations comprising: receiving access point (AP) data from a plurality of mobile devices operating in a geographic region, the AP data including signal strength measurements of AP signals received at a plurality of reference locations in the geographic region; filtering the AP data to remove outlier AP data; fitting a surface to the AP data; projecting AP data at surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the AP data at the surface control points in the image grid; encoding the boundary; encoding the AP data at the surface control points included within the boundary; generating compressed radio maps from the encoded AP data; and responsive to a request from a mobile device operating in the geographic region, sending a data packet including the compressed radio maps to the mobile device.
 13. The system of claim 12, wherein filtering AP data further comprises: identifying non-servable APs in the AP data; and excluding the non-servable APs from further processing.
 14. The system of claim 12, wherein filtering AP data further comprises: clustering the AP data; identifying outlier AP signal strength measurements based on the clustering; and excluding outlier AP signal strength measurements from further processing.
 15. The system of claim 12, wherein fitting the surface to the AP data further comprises: using bilinear interpolation to fit the surface to the AP data.
 16. The system of claim 12, wherein prior to fitting the surface to the AP data, the AP data is quantized.
 17. The system of claim 12, wherein determining the boundary further comprises: applying contour detection to the projected signal strength measurements at the surface control points; and encoding the boundary using an encoding process.
 18. The system of claim 12, wherein the geographic region is divided into a grid of contiguous cells having a first size and the plurality of reference locations are in a plurality of the contiguous cells.
 19. The system of claim 18, wherein the operations further comprise: adjusting the first cell size to a second cell size based on the AP data.
 20. The system of claim 19, wherein adjusting the first cell size to a second cell size further comprises: (a) fitting the surface to the AP data corresponding to a set of contiguous cells; (b) for the set of contiguous cells, calculating a joint likelihood of signal strength observations falling between the cells; (c) determining that the likelihood is less than a threshold; (d) dividing the set of cells in half; and repeating steps (a) through (d) until the likelihood is greater than or equal to the threshold.
 21. The system of claim 12, wherein the AP data includes AP signal strength measurements and uncertainty values corresponding to the AP signal strength measurements, and the operations further comprise: fitting surfaces to the signal strength measurements and the uncertainty values; projecting signal strength measurements and uncertainty values at the surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the signal strength measurements and corresponding uncertainty values at the surface control points in the image grid; encoding the boundary; encoding the signal strength measurements and corresponding uncertainty values at the surface control points that are included within the boundary; and generating compressed radio maps from the encoded signal strength measurements and corresponding uncertainty values and the encoded boundary.
 22. The system of claim 21, wherein the encoding scheme is at least one of predictive differential encoding, run length encoding or Rice encoding.
 23. A method comprising: receiving, by a computing device, access point (AP) data from a plurality of mobile devices operating in a geographic region, the AP data including signal strength measurements of AP signals received at a plurality of reference locations in the geographic region; fitting a surface to the AP data; projecting AP data at surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the AP data at the surface control points in the image grid; encoding the AP data at the surface control points included within the boundary; generating compressed radio maps from the encoded AP data; and responsive to a request from a mobile device operating in the geographic region, sending a data packet including the compressed radio maps to the mobile device.
 24. The method of claim 23, further comprising: identifying non-servable APs in the AP data and excluding the non-servable APs from further processing.
 25. The method of claim 23, wherein filtering AP data further comprises: clustering the AP data; identifying outlier AP signal strength measurements based on the clustering; and excluding outlier AP signal strength measurements from further processing.
 26. The method of claim 23, wherein fitting the surface to the AP data further comprises: using bilinear interpolation to fit the surface to the AP data.
 27. The method of claim 23, wherein prior to fitting the surface to the AP data, the AP data is quantized.
 28. The method of claim 23, wherein the AP data includes AP signal strength measurements and uncertainty values corresponding to the AP signal strength measurements, and the method further comprises: fitting surfaces to the signal strength measurements and the uncertainty values; projecting signal strength measurements and uncertainty values at the surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the signal strength measurements and corresponding uncertainty values at the surface control points in the image grid; encoding the boundary; encoding the signal strength measurements and corresponding uncertainty values at the surface control points that are included within the boundary; and generating compressed radio maps from the encoded signal strength measurements and corresponding uncertainty values and the encoded boundary.
 29. A system comprising: one or more processors; memory coupled to the one or more processors and configured to store instructions that when executed by the one or more processors, cause the one or more processors to perform operations comprising: receiving access point (AP) data from a plurality of mobile devices operating in a geographic region, the AP data including signal strength measurements of AP signals received at a plurality of reference locations in the geographic region; fitting a surface to the AP data; projecting AP data at surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the AP data at the surface control points in the image grid; encoding the AP data at the surface control points included within the boundary; generating compressed radio maps from the encoded AP data; and responsive to a request from a mobile device operating in the geographic region, sending a data packet including the compressed radio maps to the mobile device.
 30. The system of claim 29, the operations further comprising: identifying non-servable APs in the AP data; and excluding the non-servable APs from further processing.
 31. The system of claim 29, the operations further comprising: clustering the AP data; identifying outlier AP signal strength measurements based on the clustering; and excluding outlier AP signal strength measurements from further processing.
 32. The system of claim 29, wherein fitting the surface to the AP data further comprises: using bilinear interpolation to fit the surface to the AP data.
 33. The system of claim 29, wherein prior to fitting the surface to the AP data, the AP data is quantized.
 34. The system of claim 29, wherein the AP data includes AP signal strength measurements and uncertainty values corresponding to the AP signal strength measurements, and the operations further comprise: fitting surfaces to the signal strength measurements and the uncertainty values; projecting signal strength measurements and uncertainty values at the surface control points onto a two-dimensional image grid; determining a boundary surrounding locations of the signal strength measurements and corresponding uncertainty values at the surface control points in the image grid; encoding the boundary; encoding the signal strength measurements and corresponding uncertainty values at the surface control points that are included within the boundary; and generating compressed radio maps from the encoded signal strength measurements and corresponding uncertainty values and the encoded boundary. 